More particularly, the invention relates to an imaging method using shear waves for observing a viscoelastic medium, comprising:                an excitation steps j during which elastic shear waves are generated at an excitation locus in the viscoelastic medium by an imaging device,        an imaging step in which a set of successive images of the viscoelastic medium are determined by said imaging device during propagation of the shear wave in said viscoelastic medium.        
Document U.S. Pat. No. 7,252,004 describes an example of such a method, in which the successive images, constituting a motion picture of the propagation of the shear wave, are used to map the viscoelastic medium, by calculating at least one propagation parameter of the shear wave at one or several points in the viscoelastic medium.
Although this known method gives particularly good results, e.g. for spotting cancerous zones or the like, such method may produce images having a relatively low signal-to-noise ratio in certain circumstances, for instance in biological mediums having very complex structures producing high attenuation and diffraction (e.g. animal muscle when the shear waves are propagated transversely to muscle fibers).